During the formation of semiconductor devices, such as dynamic random access memories (DRAMs), static random access memories (SRAMs), microprocessors, etc., various layers are subject to either plasma etching, plasma deposition or both.
For example, insulating layers, such as silicon dioxide, phosphorous doped silicon dioxide, or other doped oxide, are used to electrically separate conductive layers, such as doped polycrystalline silicon, doped silicon, aluminum, refractory metal silicides, etc. It is often required that the conductive layers be interconnected through holes in the insulating layer. Such holes are commonly referred to as contact holes, i.e., when the hole extends through an insulating layer to an active device area, or vias, i.e., when the hole extends through an insulating layer between two conductive layers.
As known to those of skill in the art, various etch or deposition chemistries exist. Depending upon the layer to be etched or deposited, those of skill in the art recognize which etch chemistry or deposition chemistry to utilize.
For example, it is known to utilize plasmas containing fluorocarbons or hydrofluorocarbons to etch oxides relative to underlying silicon containing layers. Plasmas containing CF4 have been used to perform such an etch. In some cases, an inert gas such as argon is added to the etch chemistry. Using fluorocarbon or hydrofluorocarbon containing plasmas provides a means of selectively etching oxide films against an underlying silicon containing layer, i.e., the etching of the oxide film down to the underlying silicon layer without significantly etching the underlying silicon containing layer. In such a case, a high oxide to silicon etch rate ratio is required.
The mechanism responsible for the capability of fluorocarbons to accomplish high selectivity of silicon dioxide to silicon etch rate involves the combination of at least two phenomena. First, the deposition of nonvolatile residue, e.g., a polymeric containing residue, on various surfaces during the etching process, and second, the oxygen from the etching of the oxide in the process performs a particular role. While carbon containing residues are found to deposit on all surfaces inside an etch chamber containing fluorocarbon or hydrofluorocarbon plasmas, less accumulation is observed to occur on oxide surfaces, e.g., doped silicon dioxide, than on non-oxide surfaces, e.g., silicon containing surfaces such as silicon nitride, doped silicon, or polysilicon.
In other instances, etching of metal layers or metal containing layers needs to be accomplished. For example, metal layers in semiconductors can be formed of copper, aluminum, aluminum alloys such as Al—Cu, Al—Si, Al—Cu—Si, etc.
As is known to those of skill in the art, the various chemistries utilized to etch such insulation layers and/or metal layers, and in the plasma deposition of other materials are typically difficult to ignite reliably in a plasma etching apparatus. Thus, there exists a need for a plasma etching method which permits reliable ignition of the etch chemistry. Additionally, there exists a need in the art for a plasma deposition chemistry which ignites reliably.